EP0246546B1 - Telephone subscriber circuit - Google Patents

Telephone subscriber circuit Download PDF

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Publication number
EP0246546B1
EP0246546B1 EP87106878A EP87106878A EP0246546B1 EP 0246546 B1 EP0246546 B1 EP 0246546B1 EP 87106878 A EP87106878 A EP 87106878A EP 87106878 A EP87106878 A EP 87106878A EP 0246546 B1 EP0246546 B1 EP 0246546B1
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EP
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Prior art keywords
subscriber
branches
circuit
compensation
signal
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EP87106878A
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German (de)
French (fr)
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EP0246546A1 (en
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Helmuth Dipl.-Ing. Beck
Erik Dipl.-Ing. Mally
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Siemens AG Oesterreich
Siemens AG
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Siemens AG Oesterreich
Siemens AG
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M19/00—Current supply arrangements for telephone systems
    • H04M19/001—Current supply source at the exchanger providing current to substations
    • H04M19/005—Feeding arrangements without the use of line transformers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
    • H04B1/40—Circuits
    • H04B1/54—Circuits using the same frequency for two directions of communication
    • H04B1/58—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
    • H04B1/583—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa using a bridge network

Definitions

  • the invention relates to a telephone subscriber circuit of a telephone system with active switching elements with a capacitively complex input impedance, in which the signal to be sent from the system to the subscriber is amplified by two operational amplifiers operating in push-pull and via two coupling branches formed from a series connection of a capacitor and a resistor two supply resistors supplied with direct current subscriber loop is fed in, while the symmetrical subscriber signal is supplied to a subscriber amplifier via two branches of the compensation network serving to separate the signals of the two speech directions.
  • a telephone subscriber circuit of the type mentioned above is described in US Pat. No. 4,053,722, in which the compensation of interfering influences of the four-wire transmitting branch by signals arriving on the four-wire receiving branch is carried out with the aid of a separate operational amplifier, the input of which is acted upon by the signals on the four-wire receiving branch and its output signals act on an input of the subscriber amplifier, and is achieved with the aid of an equalization network, which is between the output of said operational amplifier and a reference voltage-carrying circuit point is switched on.
  • the invention has set itself the task of creating a telephone subscriber circuit that meets the stated requirements for the adaptation of the subscriber circuit and achieves this in that the coupling branches serving to feed the LF signal to be transmitted and for direct current isolation from the operational amplifiers together with two coupling resistors on the one hand and with two compensation impedances, each consisting of an RC element, on the other hand form a compensation bridge circuit, the symmetrical subscriber signal being fed to the subscriber amplifier via the coupling resistors.
  • the compensation network is transformed by transforming the impedances in such a way that its branches which serve to receive the subscriber signal contain purely ohmic resistances, while its branches which serve to compensate are provided by a simple series connection of a resistor and a capacity are formed.
  • FIG 1 of the drawing illustrated 2 shows a simplified illustration of the principle of directional separation.
  • the subscriber circuit TS assigned to the subscriber station TN is connected to the latter via the speech wires a, b.
  • the connection to the switching matrix KF located in the telephone system is established on the one hand via the input E of the subscriber circuit TS serving for the signal transmission direction from the system to the subscriber TN and on the other hand in the opposite direction via the output A.
  • the signal arriving via input E is amplified by the operational amplifier V1, which has a frequency-dependent negative feedback, and by this and the operational amplifier V ⁇ 1 in phase opposition via the capacitors C1 or C ⁇ 1 acting as isolating capacitors and via the series resistors R1 or R ⁇ 1 fed into the subscriber loop a, TN, b.
  • the opposite phase of the output signals of the operational amplifiers V1 and V ⁇ 1 comes about in that the operational amplifier V ⁇ 1 is fed via its inverting input (-) from the output signal of the operational amplifier V1. In Fig. 2 this fact is symbolized by the representation of V ⁇ 1 as a reversing element.
  • the subscriber station TN is fed from the subscriber circuit TS by the DC operating voltage via the supply resistors S and S ⁇ .
  • the signals from the subscriber station TN pass through the speech wires a, b and two ohmic coupling resistors W and W ⁇ to the inputs of a third operational amplifier V2, referred to as the subscriber amplifier, the output signal of which is fed via the output A to the switching matrix KF.
  • a third operational amplifier V2 referred to as the subscriber amplifier, the output signal of which is fed via the output A to the switching matrix KF.
  • P three connections of the circuit are designated, which conduct a fixed reference potential in operation. Two of these connections P are connected to the non-inverting inputs of the operational amplifiers V1 and V ⁇ 1, while the third is used to determine the input potential of the subscriber amplifier V2.
  • the gain of the subscriber amplifier V2 is determined by the ratio of the resistance values of its negative feedback resistor R3 or its resistance R ⁇ 3, which transmits the potential to the non-inverting
  • the output signal supplied by the subscriber amplifier V2 would be influenced by the signal fed in by the operational amplifiers V1 and V ⁇ 1 via the coupling resistors W and W ⁇ without any further measure.
  • two compensation impedances Z2, Z ⁇ 2 are therefore provided, each consisting of an RC element Rs, C2 or R ⁇ 2, C ⁇ 2.
  • the function of the compensation circuit is explained with reference to FIG. 2;
  • the impedance Z3 (Z ⁇ 3) results from the parallel connection of the supply resistance S (S ⁇ ) to half the value of the simulation impedance ZTN (subscriber impedance).
  • the voltage supplied by the amplifier V1 (V ⁇ 1) is divided by the series connection of Z1 (Z ⁇ 1) with Z3 (Z ⁇ 3), the resistance W (W ⁇ ) representing a negligible load.
  • W / Z ⁇ 2 W ⁇ / Z2
  • the capacitors C3 and C ⁇ 3 in Fig. 1 are used only for electrical isolation and have no influence on the compensation.
  • the bridge branches W, W ⁇ , Z2, Z ⁇ 2 are significantly higher-impedance than the coupling branches Z1, Z ⁇ 1 and therefore the input impedance of the subscriber circuit TS with respect to the alternating voice current from the subscriber station TN influence little.
  • the supply current source to which the supply resistors S, S ⁇ are connected is practically a short circuit.
  • the outputs of the operational amplifiers V1, V ⁇ 1 are practically at zero potential with respect to this alternating speech current, so that the input impedance of the subscriber circuit is a good approximation the series connection of the supply resistors S, S ⁇ and the parallel series connection of the impedances Z1 and Z ⁇ 1 is formed.
  • the amplification of the circuit in the direction of the subscriber TN can be set by defining the resistor R6, the amplification of the opposite direction by the resistors R3, R ⁇ 3.

Description

Gegenstand der Erfindung ist eine Fernsprechteilnehmerschaltung einer Fernsprechanlage mit aktiven Schaltelementen mit kapazitiv komplexer Eingangsimpedanz, bei der das von der Anlage zum Teilnehmer zu sendende Signal von zwei im Gegentakt arbeitenden Operationsverstärkern verstärkt und über zwei aus einer Serienschaltung eines Kondensators und eines Widerstandes gebildete Koppelzweige in die über zwei Speisewiderstände mit Gleichstrom versorgte Teilnehmerschleife eingespeist wird, während das symmetrische Teilnehmersignal über zwei Zweige des zur Richtungstrennung der Signale beider Sprechrichtungen dienenden Kompensationsnetzwerkes einem Teilnehmerverstärker zugeführt wird.The invention relates to a telephone subscriber circuit of a telephone system with active switching elements with a capacitively complex input impedance, in which the signal to be sent from the system to the subscriber is amplified by two operational amplifiers operating in push-pull and via two coupling branches formed from a series connection of a capacitor and a resistor two supply resistors supplied with direct current subscriber loop is fed in, while the symmetrical subscriber signal is supplied to a subscriber amplifier via two branches of the compensation network serving to separate the signals of the two speech directions.

Im Zuge der Bestrebungen, die Rückhörbezugsdämpfung beim Teilnehmer und damit die Übertragungsqualität zu verbessern, kommt den Bemühungen, die elektrische Anpassung der Teilnehmerschaltung an die Teilnehmer-Sprechstellen zu verbessern, eine erhöhte Bedeutung zu. In den herkömmlichen Telefonsystemen war hierfür ein Eingangswiderstand von 600 Ohm reell vorgesehen, der jedoch den Ansprüchen hoher Übertragungsqualität nicht gerecht wird.Efforts to improve the electrical adaptation of the subscriber circuit to the subscriber consoles are becoming increasingly important in the course of efforts to improve the attenuation of the listener's back and thus the transmission quality. In the conventional telephone systems, an input resistance of 600 ohms was actually provided for this, which, however, does not meet the demands of high transmission quality.

Eine Fernsprechteilnehmerschaltung der obengenannten Art ist im US-Patent 4 053 722 beschrieben, bei der die Kompensation von störenden Beeinflussungen des Vierdrahtsendezweiges durch auf dem Vierdrahtempfangszweig ankommende Signale mit Hilfe eines gesonderten Operationsverstärkers, dessen einer Eingang von den Signalen auf dem Vierdrahtempfangszweig beaufschlagt wird und dessen Ausgangssignale einen Eingang des Teilnehmerverstärkers beaufschlagen, sowie mit Hilfe eines Ausgleichsnetzwerkes erzielt wird, das zwischen dem Ausgang des genannten Operationsverstärkers und einem Bezugsspannung führenden Schaltungspunkt angeschaltet ist.A telephone subscriber circuit of the type mentioned above is described in US Pat. No. 4,053,722, in which the compensation of interfering influences of the four-wire transmitting branch by signals arriving on the four-wire receiving branch is carried out with the aid of a separate operational amplifier, the input of which is acted upon by the signals on the four-wire receiving branch and its output signals act on an input of the subscriber amplifier, and is achieved with the aid of an equalization network, which is between the output of said operational amplifier and a reference voltage-carrying circuit point is switched on.

Die Erfindung hat sich die Aufgabe gestellt, eine Fernsprechteilnehmerschaltung zu schaffen, die den angeführten Ansprüchen an die Anpassung der Teilnehmerschaltung entspricht und erzielt dies dadurch, daß die der Einspeisung des zu sendenden NF-Signales und zur Gleichstromabriegelung gegenüber den Operationsverstärkern dienenden Koppelzweige zusammen mit zwei Koppelwiderständen einerseits sowie mit zwei aus je einem RC-Glied bestehenden Kompensationsimpedanzen andererseits eine Kompensationsbrückenschaltung bilden, wobei das symmetrische Teilnehmersignal über die Koppelwiderstände dem Teilnehmerverstärker zugeführt ist.The invention has set itself the task of creating a telephone subscriber circuit that meets the stated requirements for the adaptation of the subscriber circuit and achieves this in that the coupling branches serving to feed the LF signal to be transmitted and for direct current isolation from the operational amplifiers together with two coupling resistors on the one hand and with two compensation impedances, each consisting of an RC element, on the other hand form a compensation bridge circuit, the symmetrical subscriber signal being fed to the subscriber amplifier via the coupling resistors.

Mit Hilfe dieser erfindungsgemäßen Schaltung läßt sich eine die qualitativ hochwertige Anpassung ermöglichende definierte kapazitiv komplexe Eingangsimpedanz der Teilnehmerschaltung erzielen, weil die Ausgestaltung der Schaltung in Form einer Brücke einen genauen Brückenabgleich ermöglicht. Hierbei wird auch ein hinreichend starker Speisegleichstrom ermöglicht, ohne daß eine unzumutbare hohe Speisespannung erforderlich wird, weil im Speise-Gleichstromkreis nur die Teilnehmer-Sprechstelle und die Speisewiderstände eingeschaltet sind.With the aid of this circuit according to the invention, a defined capacitively complex input impedance of the subscriber circuit which enables the high-quality adaptation can be achieved, because the configuration of the circuit in the form of a bridge enables an exact bridge adjustment. Here, a sufficiently strong DC supply current is made possible without an unreasonably high supply voltage being necessary because only the subscriber unit and the supply resistors are switched on in the DC supply circuit.

Zur Erzielung gleicher Eingangs- und Nachbildimpedanz wird gemäß einer weiteren Ausgestaltung der Erfindung das Kompensationsnetzwerk durch Transformation der Impedanzen so umgeformt, daß seine dem Empfang des Teilnehmersignals dienenden Zweige rein ohmsche Widerstände enthalten, während seine der Kompensation dienenden Zweige durch eine einfache Serienschaltung jeweils eines Widerstandes und einer Kapazität gebildet sind.To achieve the same input and after-image impedance, according to a further embodiment of the invention, the compensation network is transformed by transforming the impedances in such a way that its branches which serve to receive the subscriber signal contain purely ohmic resistances, while its branches which serve to compensate are provided by a simple series connection of a resistor and a capacity are formed.

Ein Ausführungsbeispiel der Erfindung ist in FIG 1 der Zeichnung dargestellt,
FIG 2 zeigt eine vereinfachte Darstellung des Prinzips der Richtungstrennung.An embodiment of the invention is shown in FIG 1 of the drawing illustrated
2 shows a simplified illustration of the principle of directional separation.

Die der Teilnehmerstelle TN zugeordnete Teilnehmerschaltung TS ist mit der letzteren über die Sprechadern a, b verbunden. Die Verbindung zu dem in der Fernsprechanlage befindlichen Koppelfeld KF wird einerseits über den für die Signalübertragungsrichtung von der Anlage zum Teilnehmer TN dienenden Eingang E der Teilnehmerschaltung TS und andererseits in umgekehrter Richtung über den Ausgang A hergestellt.The subscriber circuit TS assigned to the subscriber station TN is connected to the latter via the speech wires a, b. The connection to the switching matrix KF located in the telephone system is established on the one hand via the input E of the subscriber circuit TS serving for the signal transmission direction from the system to the subscriber TN and on the other hand in the opposite direction via the output A.

Das über den Eingang E ankommende Signal wird durch den Operationsverstärker V1, der eine frequenzabhängige Gegenkopplung besitzt, verstärkt und von diesem und dem Operationsverstärker Vʹ1 gegenphasig über die als Trennkondensatoren wirkenden Kondensatoren C1 bzw. Cʹ1 sowie über die Längswiderstände R1 bzw. Rʹ1 in die Teilnehmerschleife a, TN, b eingespeist. Die Gegenphasigkeit der Ausgangssignale der Operationsverstärker V1 und Vʹ1 kommt dadurch zustande, daß der Operationsverstärker Vʹ1 über seinen invertierenden Eingang (-) vom Ausgangssignal des Operationsverstärkers V1 gespeist wird. In Fig. 2 ist dieser Umstand durch die Darstellung von Vʹ1 als Umkehrglied symbolisiert.The signal arriving via input E is amplified by the operational amplifier V1, which has a frequency-dependent negative feedback, and by this and the operational amplifier Vʹ1 in phase opposition via the capacitors C1 or Cʹ1 acting as isolating capacitors and via the series resistors R1 or Rʹ1 fed into the subscriber loop a, TN, b. The opposite phase of the output signals of the operational amplifiers V1 and Vʹ1 comes about in that the operational amplifier Vʹ1 is fed via its inverting input (-) from the output signal of the operational amplifier V1. In Fig. 2 this fact is symbolized by the representation of Vʹ1 as a reversing element.

Die Teilnehmerstation TN ist aus der Teilnehmerschaltung TS von der Betriebsgleichspannung über die Speisewiderstände S und Sʹ gespeist. Die Signale der Teilnehmerstation TN gelangen über die Sprechadern a, b und über zwei ohmsche Koppelwiderstände W und Wʹ an die Eingänge eines dritten, als Teilnehmerverstärker bezeichneten Operationsverstärkers V2, dessen Ausgangssignal über den Ausgang A dem Koppelfeld KF zugeführt wird. Mit P sind drei Anschlüsse der Schaltung bezeichnet, die betriebsmäßig ein festes Referenzpotential führen. Zwei dieser Anschlüsse P sind mit den nichtinvertierenden Eingängen der Operationsverstärker V1 und Vʹ1 verbunden, während der dritte der Festlegung des Eingangspotentiales des Teilnehmerverstärkers V2 dient. Die Verstärkung des Teilnehmerverstärkers V2 ist bestimmt durch das Verhältnis der Widerstandswerte seines Gegenkopplungswiderstandes R3 bzw. seines das Potential zum nichtinvertierenden Eingang (+) übertragenden Widerstandes Rʹ3 zu den Koppelwiderständen W bzw. Wʹ.The subscriber station TN is fed from the subscriber circuit TS by the DC operating voltage via the supply resistors S and Sʹ. The signals from the subscriber station TN pass through the speech wires a, b and two ohmic coupling resistors W and Wʹ to the inputs of a third operational amplifier V2, referred to as the subscriber amplifier, the output signal of which is fed via the output A to the switching matrix KF. With P three connections of the circuit are designated, which conduct a fixed reference potential in operation. Two of these connections P are connected to the non-inverting inputs of the operational amplifiers V1 and Vʹ1, while the third is used to determine the input potential of the subscriber amplifier V2. The gain of the subscriber amplifier V2 is determined by the ratio of the resistance values of its negative feedback resistor R3 or its resistance Rʹ3, which transmits the potential to the non-inverting input (+), to the coupling resistors W and Wʹ.

Bei einer Schaltung, die nur mit den bisher angeführten Schaltungselementen ausgestattet wäre, würde ohne eine weitere Maßnahme eine Beeinflussung des vom Teilnehmerverstärker V2 gelieferten Ausgangssignales durch das von den Operationsverstärkern V1 und Vʹ1 eingespeiste Signal über die Koppelwiderstände W und Wʹ stattfinden.In the case of a circuit which would only be equipped with the circuit elements mentioned so far, the output signal supplied by the subscriber amplifier V2 would be influenced by the signal fed in by the operational amplifiers V1 and Vʹ1 via the coupling resistors W and Wʹ without any further measure.

Zur Kompensation solcher störender Einflüsse sind daher zwei Kompensationsimpedanzen Z2, Zʹ2 vorgesehen, die im einzelnen aus je einem RC-Glied Rs, C2 bzw. Rʹ2, Cʹ2 bestehen. Die Funktion der Kompensationsschaltung wird anhand von Fig. 2 erläutert; Die Impedanz Z3 (Zʹ3) ergibt sich aus der Parallelschaltung des Speisewiderstandes S (Sʹ) zum halben Wert der nachbildenden Impedanz ZTN (Teilnehmerimpedanz).To compensate for such disturbing influences, two compensation impedances Z2, Zʹ2 are therefore provided, each consisting of an RC element Rs, C2 or Rʹ2, Cʹ2. The function of the compensation circuit is explained with reference to FIG. 2; The impedance Z3 (Zʹ3) results from the parallel connection of the supply resistance S (Sʹ) to half the value of the simulation impedance ZTN (subscriber impedance).

Die vom Verstärker V1 (Vʹ1) gelieferte Spannung wird durch die Serienschaltung von Z1 (Zʹ1) mit Z3 (Zʹ3) geteilt, wobei der Widerstand W (Wʹ) eine vernachlässigbare Belastung darstellt. Zwischen dieser Teilspannung und dem Ausgang des zum ersten Verstärker inversen Verstärkers Vʹ1 (V1) liegt ein weiterer Spannungsteiler W/Zʹ2 (Wʹ/Z2), der so bemessen ist, daß sich an seinem Teilungspunkt, der mit einem Eingang des Teilnehmerverstärkers V2 verbunden ist, die Spannung Null ergibt. Damit ist auch die Differenzspannung zwischen den beiden Eingängen von V2 Null, was einer Kompensation der über den Eingang E eingespeisten Spannung entspricht.The voltage supplied by the amplifier V1 (Vʹ1) is divided by the series connection of Z1 (Zʹ1) with Z3 (Zʹ3), the resistance W (Wʹ) representing a negligible load. Between this partial voltage and the output of the amplifier Vʹ1 (V1), which is inverse to the first amplifier, there is a further voltage divider W / Zʹ2 (Wʹ / Z2), which is dimensioned such that at its division point, which is connected to an input of the subscriber amplifier V2, the voltage is zero. The differential voltage between the two inputs of V2 is thus zero, which corresponds to a compensation of the voltage fed in via input E.

Die Kondensatoren C3 bzw. Cʹ3 in Fig. 1, dienen lediglich der galvanischen Trennung und haben keinen Einfluß auf die Kompensation.The capacitors C3 and Cʹ3 in Fig. 1 are used only for electrical isolation and have no influence on the compensation.

Bezüglich der Bemessung aller Widerstände bzw. Impedanzen ist zunächst davon auszugehen, daß die Brückenzweige (W, Wʹ, Z2, Zʹ2) wesentlich hochohmiger sind als die Koppelzweige Z1, Zʹ1 und daher die Eingangsimpedanz der Teilnehmerschaltung TS in Bezug auf den Sprechwechselstrom von der Teilnehmerstelle TN wenig beeinflussen. Für diesen Sprechwechselstrom stellt die Speisestromquelle, an die die Speisewiderstände S, Sʹ angeschlossen sind, praktisch einen Kurzschluß dar. Ebenso liegen die Ausgänge der Operationsverstärker V1, Vʹ1 in Bezug auf diesen Sprechwechselstrom praktisch auf Nullpotential, so daß die Eingangsimpedanz der Teilnehmerschaltung in guter Näherung durch die Serienschaltung der Speisewiderstände S, Sʹ und durch die dazu parallele Serienschaltung der Impedanzen Z1 und Zʹ1 gebildet wird.With regard to the dimensioning of all resistances or impedances, it can initially be assumed that the bridge branches (W, Wʹ, Z2, Zʹ2) are significantly higher-impedance than the coupling branches Z1, Zʹ1 and therefore the input impedance of the subscriber circuit TS with respect to the alternating voice current from the subscriber station TN influence little. For this alternating speech current, the supply current source to which the supply resistors S, Sʹ are connected is practically a short circuit. Likewise, the outputs of the operational amplifiers V1, Vʹ1 are practically at zero potential with respect to this alternating speech current, so that the input impedance of the subscriber circuit is a good approximation the series connection of the supply resistors S, Sʹ and the parallel series connection of the impedances Z1 and Zʹ1 is formed.

Abschließend ist noch zu erwähnen, daß die Verstärkung der Schaltung in Richtung zum Teilnehmer TN durch Festlegung des Widerstandes R6, die Verstärkung der Gegenrichtung durch die Widerstände R3, Rʹ3 eingestellt werden kann.Finally, it should also be mentioned that the amplification of the circuit in the direction of the subscriber TN can be set by defining the resistor R6, the amplification of the opposite direction by the resistors R3, Rʹ3.

Im einzelnen hat sich für die erfindungsgemäße Schaltung die folgende Dimensionierung bewährt:

Figure imgb0001
In particular, the following dimensioning has proven itself for the circuit according to the invention:
Figure imgb0001

Claims (2)

  1. Telephone subscriber circuit of a telephone exchange comprising active switching elements with capacitive complex input impedance, in which the signal to be transmitted from the exchange to the subscriber is amplified by two operational amplifiers operating in push-pull and is fed into the subscriber loop, supplied with direct current via two feed resistors, via two coupling branches formed by a series connection of a capacitor and of a resistor whilst the balanced subscriber signal is supplied to a subscriber line amplifier via two branches of the compensation network used for separating the direction of the signals of both speech directions, characterized in that the coupling branches (R1,C1 and Z1; R'l, C'1 and Z'1), used for feeding-in the AF signal to be transmitted and for direct-current isolation from the operational amplifiers (V1, V'1), together with two coupling resistors (W, W'), on the one hand, and with two compensation impedances (Z2, Z'2) consisting of one RC section each (R2, C2; R'2, C'2), on the other hand, form a compensation bridge circuit, the balanced subscriber signal being supplied to the subscriber line amplifier (V2) via the coupling resistors (W, W').
  2. Circuit according to Claim 1, characterized in that, assuming identical input and balancing impedance, the compensation network is transformed by transformation of the impedances in such a manner that its branches (W, W') used for receiving the subscriber signal contain purely ohmic resistors whilst its branches (Z2, Z'2) used for the compensation are formed by a simple series circuit of in each case one resistor and capacitor (R2,Z2; R'2, Z'2).
EP87106878A 1986-05-23 1987-05-12 Telephone subscriber circuit Expired - Lifetime EP0246546B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT1380/86 1986-05-23
AT0138086A AT386307B (en) 1986-05-23 1986-05-23 TELEPHONE PARTICIPATION

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EP0246546A1 EP0246546A1 (en) 1987-11-25
EP0246546B1 true EP0246546B1 (en) 1991-05-29

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US (1) US4914693A (en)
EP (1) EP0246546B1 (en)
AR (1) AR241564A1 (en)
AT (2) AT386307B (en)
BR (1) BR8702641A (en)
DE (1) DE3770335D1 (en)
DK (1) DK257187A (en)
FI (1) FI85930C (en)
PT (1) PT84929B (en)

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US4053722A (en) * 1976-10-04 1977-10-11 The United States Of America As Represented By The Secretary Of The Navy Solid state two-wire/four-wire converter with common battery
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US4283604A (en) * 1979-06-04 1981-08-11 Tellabs, Inc. Current source circuits with common mode noise rejection
FR2478908B1 (en) * 1980-03-21 1984-08-03 Thomson Csf Mat Tel
US4387273A (en) * 1980-08-25 1983-06-07 International Telephone And Telegraph Corporation Subscriber line interface circuit with impedance synthesizer
CA1154185A (en) * 1981-01-23 1983-09-20 Patrick R. Beirne Subscriber line interface circuit
CA1200335A (en) * 1984-02-13 1986-02-04 Stanley D. Rosenbaum Active impedance line feed circuit
JPS61244191A (en) * 1985-04-22 1986-10-30 Nec Corp Subscriber's circuit

Also Published As

Publication number Publication date
US4914693A (en) 1990-04-03
DK257187A (en) 1987-11-24
PT84929A (en) 1987-06-01
PT84929B (en) 1990-02-08
AR241564A1 (en) 1992-08-31
EP0246546A1 (en) 1987-11-25
ATE64052T1 (en) 1991-06-15
FI872277A0 (en) 1987-05-22
ATA138086A (en) 1987-12-15
DK257187D0 (en) 1987-05-21
FI85930C (en) 1992-06-10
BR8702641A (en) 1988-02-23
FI872277A (en) 1987-11-24
DE3770335D1 (en) 1991-07-04
AT386307B (en) 1988-08-10
FI85930B (en) 1992-02-28

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